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LECTURE 13 - AEOLIAN DEPOSITS AND LANDFORMS LOESS DEPOSITS Characteristics Consist of wind-deposited silt , accompanied by some clay and some fine sand. Mantels surface and has porosity usually >50% . Characterized by extremely well-sorted , fine grained sediment mostly composed of silt-size quartz grains , but may also be highly calcareous. Particles angular and generally range between 20 and 60 microns in diameter, although considerable finer-sized material may also be present. Highly cohesive , having been consolidated by secondary precipitation of calcium carbonate. Leads to gullied topography and steep, almost vertical cliffs . Origin Derived from glacier rock flour in outwash plains during periods of continental glaciation (in Illinois). Can be transported great distances beyond source area (Bermuda). Also produced in so-called “warm” desert areas due to combined action of frost and salt weathering (in Central Asia). More poorly sorted then in periglacial environments. Sometimes extensively reworked and redeposited by colluvial and alluvial processes. Most accumulations are composite in age and include paleosols. Thickness and grain size increases exponentially towards source area.
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May contain large number of mollusca useful for dating deposit and analyzing environment of sediment deposition.
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